1. Field of the Invention
The present invention generally relates to a disc cartridge, and more particularly, relates to a disc cartridge which can be applied to an optical disc system. In the optical disc system of the present invention, an embedded member for relieving the shock in the gap between the shutter and the case of the optical disc system is provided. In addition, a sheet-like member is provided for cleaning the surface of an optical disc accommodated in the optical disc system so that the recording and playback characteristics can be effectively prevented from being deteriorated by the effects of dust particles and other foreign materials adhered to the surface of the optical disc.
2. Description of the Prior Art
The DVD (Digital Versatile Disc) has been proposed as an optical disc for use in a conventional optical disc drive for recording information onto the disc at a high recording density. By irradiation of a laser beam with a wavelength of 650 nm by means of an optical system with a numerical aperture of 0.6 upon a DVD, one side of the optical disc can be used for recording data of up to 2.6 MB in length. As a result, one side of the optical disc can be used for recording a video signal having a playback time of about 1 hour.
In such an optical disc drive, the desired data is recorded on and reproduced from an optical disc by adopting a non-contact technique. The optical disc is normally kept in a plastic case for preventing finger prints from being imprinted on the surfaces of the disc and for extended storage of the disc. When using the optical disc, the disc is removed from the plastic case and mounted on the optical disc drive.
Of course, in the case of a video tape recorder for home applications, the basic recording time is 2 hours. In order to allow the user to use an optical disc drive in the same way as the home video tape recorder, it is necessary for the optical disc drive to be capable of recording an even larger amount of data. In addition, in order to allow processing, such as editing to be performed through effective utilization of characteristics of the optical disc including a random access function, it is necessary to increase the recording time of the video signal to a length on the order of 3 hours. In a DVD system having such capabilities, it is necessary for the optical disc to be able to record data of up to about 8 MB.
As a result, it is necessary to record a video signal at a high recording density in the optical disc drive by means of an optical system having a high numerical aperture. As for the optical disc, it is necessary to further reduce the thickness of a light transmissive layer which allows a laser beam to pass therethrough in order to decrease the effect of a skew (bend or warp). However, deterioration of the recording and playback characteristics may result which is caused by dust particles and other foreign particles adhering to the surfaces of the optical disc.
In order to explain the problem described above in more detail, results of an experiment performed by using an optical disc drive having a numerical aperture of 0.8 and a light transmissive layer with a thickness of 0.1 mm are compared with results of an experiment performed by using an optical disc drive having a numerical aperture of 0.6 and a light transmissive layer with a thickness of 0.6 mm. As is shown in FIG. 25, if the numerical aperture is increased while the thickness of the light transmissive layer is reduced, even microscopic dust and other foreign particles adhered to the surfaces of the optical disc can cause a burst error. Such dust and other foreign particles continually accumulate on the surfaces of the optical disc. As a result, the recording and playback characteristics of the optical disc drive gradually deteriorate over extended use of the disk drive.